In the field of integrated circuits, ensuring proper data input is necessary. Toward this end, data input margins and impedance calibration may play a role. Typically, a termination resistor having the same resistance value as a characteristic impedance is coupled to a receiving end or a transmitting end of a semiconductor device. The termination resistor suppresses the reflection of signals transferred through the transmission channel by matching the impedance of the receiving end or the transmitting end with the characteristic impedance of the transmission channel.
A conventional termination resistor is installed outside a semiconductor chip. Recently, an on-die termination (ODT) circuit in which a terminal resistor is installed inside a semiconductor chip has been used. Since an ODT circuit includes a switching circuit which performs an on/off operation to control a current flowing thereinside, power dissipation is lower than that of a termination resistor installed outside a semiconductor chip. The resistance value of the ODT circuit changes according to process, voltage and temperature (PVT) variation. Thus, before use, the resistance value of the ODT circuit is calibrated by using an impedance calibration (ZQ calibration) circuit.